The present invention relates to structural members such as girders which rest on spaced apart supports and which are capable of supporting relatively large payloads.
Girders as such are well-known in the art and widely used for spanning the distance between spaced apart supports such as upright building walls while carrying a load, e.g. a flat building roof and roof loads such as snow or water. The actual construction of such girders varies widely depending on their span, the payload and the cost of materials. Generally, however, the greater span and/or the payload the more intricate is the construction of the girders. Thus, high strength girders for very large loads and/or spans invariably are fabricated from a variety of I-beams, channels, angles, plate and the like. Such girders are relatively heavy and, in view of today's high material costs, are expensive for this reason alone. In addition, they require a great amount of labor to assemble them which further increases their cost. Nevertheless, such girders have found wide-spread use and they continue to be used inspite of their cost because for many applications no feasible alternatives exist.
For light forms of constructions in which the payload and/or girder length is relatively small substantially simplified girders can be used. U.S. Pat. Nos. 1,604,150; 2,746,580 or 3,122,224 are exemplary of such structures. For example, the first mentioned patent proposes a girder for light forms of construction such as for carrying trellis which is made of a pair of parallel, spaced apart flanges which are interconnected by a web member that extends between the flanges in a zigzag fashion. The flanges and the web are provided with longitudinally extending, intermittent, relatively narrow channels to achieve a nesting of all components of the girder and to rigidify it.
Although the girder disclosed in that patent, as well as in the others eliminates a substantial portion of the cost which results from fabricating girders of multiple welded, bolted, riveted or the like components, they have not replaced fabricated girders for high strength applications. The exact reasons for this are unclear, but it is apparent that they include the fact that the profiles suggested in the patents are incapable of carrying substantial loads over the desired spans. In addition, it is likely that the connections between the flanges and the intermediate web members could not be made sufficiently strong to carry the loads because of the relatively small contact points between them which are unable to safely transmit large loads.